The Shepherds were out in the fields watching their flocks by night.
Read Genesis 35:19-20. It tells how Rachel died "and was buried on the way to Ephrath (that is, Bethlehem)" and how Jacob went on and "pitched his tent beyond the tower of Eder."
Then read Jeremiah 31:15-16. It tells about "Rachel weeping for her children". It is at Ramah that the people of Judah were gathered, chained and roped together, and led off to exile in Babylon. But verse 16 says, "Keep your voice from weeping . . . they shall come back from the land of the enemy."
Putting those two passages together (1) God gives hope for the mothers of Bethlehem whose children were killed by Herod -- "they shall come back." But also (2) the Rabbis expected that the first announcement of the coming Messiah would be at "Migdol Eder;" the "tower of Eder." Eder means flock (as in flock of sheep), so "Migdol Eder" means "Tower of the Flock." Look up Luke 2:8-11 and see if they were right.
Why were the shepherds out in the fields at night? Most sheep are brought into the sheepfold where they are safer. But Bethlehem is close to Jerusalem. Sheep that were destined to be sacrificial sheep at the Temple had to be kept outside, in nature not in buildings all the time. Shepherds built towers to more easily watch their sheep.
So the angels went to shepherds watching over sacrificial sheep to tell them about the One Lamb, the Lamb of God who takes away the sin of the world. This is amazingly appropriate, isn't it?